Sintered electrodes for cold cathode tubes and cold cathode tubes provided with this electrode have hitherto been used, for example, as backlights for liquid crystal display devices. In addition to high luminance and high efficiency, a long service life is required of such cold cathode tubes for liquid crystal applications.
In general, the construction of cold cathode tubes useful as backlights for liquid crystal applications is such that very small amounts of mercury and rare gas are filled into a glass tube comprising a fluorescent substance coated onto the inner surface thereof, and an electrode and a lead-in wire (for example, KOV+dumet wire) are mounted on both ends of this glass tube. In such cold cathode tubes, upon the application of voltage to both end electrodes, mercury sealed in the glass tube is evaporated, resulting in emission of ultraviolet light which is absorbed by the fluorescent substance to emit light.
Nickel materials have hitherto been mainly used as the electrode. This Ni (nickel) electrode, however, is disadvantageous in that a cathode drop voltage necessary for electron emission from the electrode to a discharge space is relatively high and, in addition, the occurrence of the phenomenon of the so-called “sputtering” is likely to deteriorate the service life of the lamp. The sputtering phenomenon refers to a phenomenon that the electrode undergoes ion collision during lighting of the cold cathode tube to cause scattering of an electrode material, and the scattered material and mercury and the like are accumulated on the internal wall surface within the glass tube.
Mercury is introduced into the sputtering layer formed by the sputtering phenomenon, making it impossible to utilize mercury in luminescence. Accordingly, when the cold cathode tube is lighted for a long period of time, the luminance of the lamp is extremely lowered to reach the end stage of the service life. Therefore, if the sputtering phenomenon could be reduced, the mercury consumption could be suppressed and, thus, the service life could be prolonged even in the same mercury sealing amount.
This has led to an attempt to simultaneously realize both cathode voltage drop reduction and sputtering suppression. In a recent effort, an electrode design, in which an electrode in a closed-end cylindrical form is adopted to attain a holocathode effect for realizing both cathode voltage drop reduction and sputtering suppression, has been proposed (Japanese Patent Laid-Open No. 176445/2001). Further, a proposal has been made in which, instead of nickel in the prior art technique, Mo (molybdenum) or Nb (niobium) or the like, which can lower the cathode voltage drop by about 20V, has been used as the electrode material.
Patent document 1: Japanese Patent Laid-Open No. 176445/2001